I was doing some general internet browsing and stumbled across Blue Devil head gasket sealer which advertises permanent fix to any head gasket leak. The reviews on the internet also seem to be quite positive with most customers claiming the product worked for them.

I got to thinking and my question is, in a hypothetical scenario: what would happen if you added this product or other similar products to a car that is not showing any obvious signs of head gasket problems? Would there be any negative consequences?

  • 2
    Other than the hole in your pocket book? Probably not. I don't know for sure, but since it doesn't harm your system in the first place if you did have a leak, I'd think there'd be no ill effects for using it when you don't. Really though, to what end? To me you're just wasting money. – Pᴀᴜʟsᴛᴇʀ2 Aug 19 '18 at 1:34
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    If you want it to sit there waiting for a leak ie a pre-emptive repair like some tire-slime products - it won't. As Paulster2 says a waste of money. – Solar Mike Aug 19 '18 at 6:58

Adding "Blue Devil" sealer or any other non-approved chemicals to a motor vehicle is not necessary, a waste of money, can be dangerous (destructive) to the engine and may void the new car warranty. I've been doing auto repair since 1974. :-)


A modern head gasket in a cast iron block/aluminum headed engine does not actually seal in the way that say a jar seal does or a cap on a pop bottle. Instead you have a set of TTY bolts that are in essense giant springs that put a constant force of many tons on the gasket.

Stop leak gasket sealer is based on the notion that a gasket is like a paper gasket it is a fixed thing and it degrades over time and gets "loose" The stop leak works its way into the gasket filling up the voids. Old head gaskets might have worked that way but not modern ones since the TTY force insures that a constant pressure is on the gasket even if the gasket gets squashed down.

  • Tons? Really ? Pressure is force applied divided by area so if there are 12 bolt heads 1cm square applying pressure and a cylinder head of 25cm by 60cm what do you think? – Solar Mike Aug 19 '18 at 12:09

It very much depends on how the sealer works. Some more modern sealers are liquid until they come into contact with the kinds of conditions found within the cylinders during combustion at which point they "go off". I am lead to believe that "Steel Seal", a brand available in the UK works in this way. This therefore makes it effective for sealing a gasket that's blown between a water jacket and a combustion chamber. This type of sealant wouldn't do anything to a car which didn't have a head gasket leak.

Other sealers work by adding a material or hardening in some way. They may, for example, add some sort of "silt" to the coolant system which is deposited around the system. Adding too much of this is enough to cause blockages in heater matrixs and radiators.

Before doing anything to repair a non-existent head gasket leak, have either a compression test or leak down test carried out as this will generally be cheaper than one of these liquid gasket repair fluids.

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